You have probably seen the ads on Saturday morning television
proclaiming the amazing abilities of the "Super Ultra
Road-rippin' Devastator" or some other radio controlled
(RC) car. And you may have seen people at the park flying
a model airplane
or controlling a miniature boat sailing serenely across a
A typical radio controlled toy
In this edition of HowStuffWorks,
you will learn all about radio
control. You will find out what frequencies are used for RC
toys, what the different components are and how they all work
together. You will also learn what the difference between
radio control and remote control is when talking about toys or
Types of RC Toys
RC toys come in a large
variety of models, including:
While the mechanics of how they operate can differ greatly
between different toys, the basic principle is the same. All
radio controlled toys have four main parts:
sends a control signal to the receiver
waves. To understand how the transmitter and receiver
communicate together, go to the next page...
- Transmitter - You hold the transmitter in your
hands to control the toy. It sends Radio
waves to the receiver.
- Receiver - An antenna and circuit board inside
the toy receives signals from the transmitter and activates
motors inside the toy as commanded by the transmitter.
- Motor(s) - Motors can
turn wheels, steer the vehicle, operate propellers, etc.
- Power source
RC toys typically have a
small handheld device that includes some type of controls and
the radio transmitter. The transmitter sends a signal over a
to the receiver in the toy. The transmitter has a power
source, usually a 9-volt battery,
that provides the power for the controls and transmission of
the signal. The key difference between radio controlled and
remote controlled toys is that remote controlled toys have a
wire connecting the controller and the toy, while radio
control is always wireless.
A typical RC car transmitter
Most RC toys operate at either 27 MHz or 49
MHz. This pair of frequencies has been allocated by the
FCC for basic consumer items, such as garage door openers,
walkie-talkies and RC toys. Advanced RC models, such as the
more sophisticated RC airplanes, use 72-MHz or 75-MHz
The majority of RC toys are labeled with the frequency
range they operate in. For example, the RC truck below has a
label designating it as a 27-MHz model.
This truck operates at 27 MHz.
Most RC toy manufacturers make versions of each model for
both frequency ranges (27 MHz and 49 MHz). That way, you can
operate two of the same model simultaneously, for racing or
playing together, without having to deal with interference
between the two transmitters. Some manufacturers also provide
more specific information about the exact portion of the frequency
band that the toy operates in. A good example is Nikko
of America, who offers the option to create racing sets of
up to six toys with each model tuned to a different part of
the 27-MHz frequency range.
Transmitters range from single-function simple controllers
to full-function controllers with a wide range of options. An
example of a single-function controller is one that
makes the toy go forward when the trigger is pressed and
backward when it is released. To stop the toy, you have to
actually turn it off.
Most full-function controllers have six controls:
In most full-function
controllers, not pressing any buttons or turning any knobs
causes the toy to stop and await further commands. Controllers
for more advanced RC systems often use dual joysticks
with several levels of response for precise control.
- Forward and Left
- Forward and Right
- Reverse and Left
- Reverse and Right
Let's take a closer look at
the RC truck we saw above. We will assume that the exact
frequency used is 27.9 MHz. Here's the sequence of events that
take place when you use the RC transmitter:
- You press a trigger to make the truck go forward.
- The trigger causes a pair of electrical contacts to
touch, completing a circuit connected to a specific pin of
an integrated circuit (IC).
- The completed circuit causes the transmitter to transmit
a set sequence of electrical pulses (see How Radio
Works for details).
Each sequence contains a short group of synchronization
pulses, followed by the pulse sequence. For our truck, the
synchronization segment -- which alerts the receiver
to incoming information -- is four pulses that are 2.1
milliseconds (thousandths of a second) long, with
700-microsecond (millionths of a second) intervals. The
pulse segment, which tells the antenna what the new
information is, uses 700-microsecond pulses with
A typical RC signal transmission
Here are the pulse sequences used in the pulse
- Forward: 16 pulses
- Reverse: 40 pulses
- Forward/Left: 28 pulses
- Forward/Right: 34 pulses
- Reverse/Left: 52 pulses
- Reverse/Right: 46 pulses
If you look inside the
RC truck, you will see that it is very simple: two electric
motors, an antenna, a battery
pack and a circuit board!
- The transmitter sends bursts of radio waves that
oscillate with a frequency of 27,900,000 cycles per second
(27.9 MHz). If you have read How Radio
Works, you will recognize this as pulse
- The truck is constantly monitoring the assigned
frequency (27.9 MHz) for a signal. When the receiver
receives the radio bursts from the transmitter, it sends the
signal to a filter that blocks out any signals picked up by
the antenna other than 27.9 MHz. The remaining signal is
converted back into an electrical pulse sequence.
- The pulse sequence is sent to the IC in the truck, which
decodes the sequence and starts the appropriate motor. For
our example, the pulse sequence is 16 pulses (forward),
which means that the IC sends positive current to the motor
running the wheels. If the next pulse sequence were 40
pulses (reverse), the IC would invert the current to the
same motor to make it spin in the opposite direction.
- The motor's shaft actually has a gear on the
end of it, instead of connecting directly to the axle. This
decreases the motor's speed but increases the torque,
giving the truck adequate power through the use of a small
- The truck moves forward.
A look at the inside of the truck
One motor turns the front wheel right or left, while the
other motor turns the rear wheels to go forward or backward.
The circuit board contains the IC chip, amplifier and radio
receiver. A few simple gears connect the motors to the wheels.
It is really amazing how versatile the range of movement is
with so few components.
On the next page, you will get a good look at the
unassembled components of an RC car.
Anatomy of an RC Car
- The body of the car consists of a lower chassis, that
holds all the mechanical and electronic components, and a
shell that fits on top of the chassis. The shell provides
most of the distinctive style of the car.
- Inside the car, you will find a circuit board with
resistors and diodes,
as well as the IC that controls the motors. The radio
receiver consists of a crystal that oscillates
at a specific frequency, inductors
and an antenna.
- The electric motors
receive power from the batteries.
The flow of the power is regulated by the IC.
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